Implantable tissue stimulator

ABSTRACT

An implantable tissue stimulator comprising a metal case enclosing a battery and a pulse generating circuit powered thereby, in which the circuit includes a terminal common to the case and a stimulating terminal extending through and insulated from the case, a flexible probe assembly comprising an exposed electrode adapted to be placed in proximity to and in electrical contact with tissue to be stimulated, and an elongated flexible insulated cable connecting the electrode to a connector part adapted to be secured to the stimulating terminal during implantation.

United States Patent Cole [54] IMPLANTABLE TISSUE STIMULATOR [72]Inventor: Addison D. Cole, Natick, Mass.

[73] Assignee: Adcole Corporation, Waltham,

Mass. a

[22] Filed: June 1, 1970 [21] Appl, No.: 41,890

[52] 0.8. CI ..128/4l9 P, 128/419 C [51] Int. Cl. ..A6ln H36 [58] Fieldof Search ..l28/404,418,4l9 P,419 R, 128/421, 422

[56] References Cited UNITED STATES PATENTS 3,486,506 12/1969 Auphan..128/419 P 3,454,012 7/1969 Raddi 128/419 P 3,253,595 5/1966 Murphy,Jr. et al.... 128/419 P 3,357,434 12/1967 Abell ..12 8/419 P 1513,683,932 51 Aug. 15, 1972 Frasier ..128/419 P 3,348,548 lO/ 1967Chardack ..128/4l9 P 3,472,234 10/ 1969 Tachick 128/419 P 3,421,511l/l969 Schwartz et a1. 128/418 Primary Examiner-William E. KammAttorney-Rich & Ericson [57] ABSTRACT An implantable tissue stimulatorcomprising a metal 'case enclosing a battery and a pulse generatingcircuit powered thereby, in which the circuit includes a terminal commonto the case and a stimulating terminal extending through and insulatedfrom the case, a flexi ble probe assembly comprising an exposedelectrode adapted to be placed in proximity to and in electrical contactwith tissue to be stimulated, and an elongated flexible insulated cableconnecting the electrode to a 4 connector part adapted to be secured tothe stimulating terminal during implantation.

5 Claims, 11 Drawing Figures Patented Aug. 15, 1972 2 Sheets-Sheet 1 5PULSE JUL GENERATOR IZF H BLOCKING OSCILLATOR FIG. I

FIG. 4

FIG.6

INVENTOR ADDISON D. COLE BY Maw ATTORNEYS Patented Aug. 15, 19723,683,932

11 Sheets-Sheet 2 FIG. l0

AINVENTOR ADDISON o. COLE I ATTORNEYS IMPLANTABLE TISSUE STIMULATOR Myinvention relates to electrical tissue stimulators,

and particularly to a novel implantable stimulator.

Great strides have been made in the development of cardiac prostheticdevices for supplanting, supplementing or controlling the action of theheart during periods of malfunction, disease or radical functionaldisruption, as during surgery or the like. In particular, a demand hasarisen for heart pacers that will deliver electrical stimulating pulsesin place of natural pulses that fail to occur under various pathologicalconditions. For many purposes, it is essential that this supplementarystimulating function be performed over relatively long periods of timeinconsistent with the use of external circuits and power suppliestranscutaneously connected to the stimulated tissue. Thus, a fullyimplantable, selfcontained pacer would be highly desirable.

One of the principal obstacles to the construction of a practicalimplantable pacer is the physical size of the container for the pulsegenerating circuit and its power source. There are numerous requirementson such a container that are difficult to meet without excessive sizeand weight. First, the container must present an exterior that is fluidtight, electrically insulates the contained circuit, and is chemicallyinert and thermally inactive. Those requirements are generally met byencapsulating the electrical contents of the container in athermoplastic insulating material, through which insulated electricalconnector parts must be passed. In general, the power supply and theelectronic pulse generating circuit must be implanted in the body at adistance from the preferred site for stimulation. Thus, the stimulatingelectrode or electrodes must be connected to the power package by along, flexible, insulated cable. The necessities of surgery dictate thatthe assembly be separated before implantation, i. e., by providing aseparable electrical connector between the power package and theflexible probe carrying the stimulating electrodes, so that thoseelements can be separately installed and then connected together afterimplantation. Since the connectors must maintain a fluid seal betweenthe internal electrical terminals of the pulse generating circuit andthe body, a relatively rugged, and therefore massive, connectorconstruction has been employed. The result has been that practicalpacers have tended to be limited in design by the maximum size andweight thatcould be tolerated, rather than by the performance criteriathat would govern if space and weight were no object. The objects of myin vention are to decrease the size and weight of implantable cardiacpacers while improving their efficiency and service life.

Briefly, the above and other objects of my invention are attained by anovel pacer construction in which the container for the power supply andpulse generating circuits comprises a sealed metal canister that alsoserves as one electrode of the stimulating circuit. This container isnot encapsulated in an insulating plastic material, nor are theelectronic components which it surrounds preferably encapsulated. Thecontainer preferably comprises a relatively thin, flat rectangular metalpackage formed with retaining means for holding a circuit board ofinsulating material inside the container in a fixed position. Mounted onthis board are the power supply and pulse generator circuit. The largestsingle electrical element is the power supply, preferably a single diskshaped mercury-zinc storage battery. Next in size is a pulse transformerforming the output element of the pulse generator. The battery andtransformer together determine the basic size of the housing, as othernecessary circuit elements may be considerably smaller and thus readilymounted in spaces available adjacent the larger components. Two externalmounting posts are preferably connected to the housing. These posts areadapted to cooperate with corresponding recesses in a thermoplasticconnector plug. One mounting post contains a central insulated conductoradapted to be connected in circuit with the pulse transformer, and toengage a contact in the connector plug that is in turn connected,through a flexible insulated conductor, to a stimulating electrode.Preferably, a fastener is provided to fix the connector plug to themetallic housing after assembly, to prevent the parts from workingloose. Desirably, a passage is provided in the connector and theadjoining flexible probe assembly to admit a stiffening wire tofacilitate insertion of the probe into a selected body sinus, such as anartery or the like.

The manner in which the apparatus of my invention is constructed, andits mode of operation, will best be understood in the light of thefollowing detailed description, together with the accompanying drawings,of a preferred embodiment thereof.

In the drawings,

FIG. 1 is a wiring diagram of a conventional cardiac pacer of the typewith which my invention is concerned;

FIG. 2 is a composite waveform diagram illustrating the operation of thecircuit of FIG. 1;

FIG. 3 is a schematic fragmentary elevational view of a power supply andpulse generating circuit forming a part of the apparatus of myinvention;

FIG. 4, is a schematic cross-sectional view of the ap paratus of FIG. 3,taken substantially along the lines 4-4 in FIG. 3;

FIG. 5 is a schematic exploded perspective sketch of a pacer housingassembly forming a part of the apparatus of my invention;

FIG. 6 is a schematic cross-sectional view of the apparatus of FIG. 5,taken substantially along the lines 6-6 of FIG. 5 and showing theapparatus of FIGS. 3 and 4 in place;

FIG. 7 is a schematic elevational view, with parts shown in crosssection and parts broken away, of a cardiac pacer in accordance with myinvention;

FIG. 8 is a detailed cross-sectional view, on an enlarged scale, of aportion of the apparatus of FIG. 7, taken essentially along the lines8-8 in FIG. 7;

FIG. 9 is a plan view of the apparatus of FIG. 7 with the connectorremoved, taken essentially along the lines 9-9 in FIG. 7;

FIG. 10 is an enlarged cross-sectional view of a portion of theapparatus of FIG. 7, showing parts in more detail and including aportion of a stiffener assembly; and

FIG. 11 is an end view, taken essentially along the lines 1lll in FIG.10, showing a detail of the stiffener assembly.

Referring to FIG. 1, l have shown the essential elements of a fixed-ratecardiac pacer. A primary source of energy 1 conventionally comprises oneor more storage batteries. I prefer to employ a single, disk-likemercury-zinc storage battery for the purpose. The battery 1 energizes apulse forming network comprising a blocking oscillator 3, a pulsegenerator 5, and a pulse transformer generally designated 7 and having aprimary winding 9 and a secondary winding 1 1. The secondary winding 1 1is adapted to be connected in circuit with the heart by means ofelectrodes 13 and 15. As will appear, I prefer to make one of theelectrodes such as 13 serve to conduct current directly to the site tobe stimulated, and to make the second electrode 15 common to oneterminal of the battery 1, preferably the negative terminal.

FIG. 2 illustrates the basic mode of operation of the circuit of FIG. 1.The blocking oscillator 3 produces a ramp signal, FIG. 2(a), having aperiod equal to that of the heart beat to be simulated, i.e., typically832 milliseconds for a normal 72 per minute heartbeat. The trailing edgeof the ramp signal causes the pulse generator to produce a stimulatingpulse, FIG. 2b, of preferably about 4 volts at 13 milliamperes for about/4 millisecond. Average output power dissipation is thus about 31microwatts.

FIGS. 3 and 4 illustrate the mounting of the principal parts of thecircuit of FIG. 1 in accordance with my invention. The largest elementis the battery 1, both as to size and weight. The next element in pointof size is the pulse transformer 7. These elements are preferablymounted in adjacent, spaced relation on a board 17, of any suitableinsulating material such as phenolic resin, glass fiber tilled expoxyresin, or the like. Any suitable mounting or adhesive means, such as anepoxy resin or the like, may be employed to secure the parts together.Other electrical components, such as capacitors, resistors, diodes,transistors and the like, being of smaller size, may be disposed aboutthe board 17 in any convenient manner and interconnected by printedcircuits mounted on the board 17, by separate insulated conductors, orby other conventional techniques.

FIG. illustrates the manner in which the board 17 and its associatedelectrical parts is mounted and contained. A two-part housing is formedby a generally rectangular container 19, of stainless steel or the like,having one open end, and an end cap generally designated 21, also ofstainless steel or the like. The end cap is adapted to engage thecontainer 19 fairly snugly, and to be sealed in place by welding, aswill appear.

The container 19 is arranged to receive the board 17 and its associatedelectronic parts. As shown in FIGS. 5 and 6, end walls 23 of thecontainer 19 are formed with depressions such as 25, creating ribs 27 toengage the edges of the board 17. A small amount of epoxy resin or otherdesired adhesive is preferably used to further secure the board 17within the container 19, and to inhibit vibration. I

As best shown in FIGS. 5 and 10, the end cap 21 is formed withdownwardly depending side flanges 31 that are adapted to engage theinner sides of the container 19. After assembly and electricalconnection of the other parts, in a manner to appear, the flanges 31 ofthe end plate 21 are welded to the sides of the container 19, with theparts in the position shown in FIG. 10, to form a sealed seam.

Referring to FIGS. 5, 7 and 10, the end cap 21 is formed with threeupstanding annular flanges 33, 35 and 37. To the flange 33 is welded anupstanding post 39, of stainless steel or the like. An externallysimilar conductor post 41 is welded into the flange 37. To the flange 35is welded a connector 43 that is threaded as indicated at 45 in FIG. 10to receive a cooperatively threaded bolt 47.

Referring to FIGS. 7 and 10, a separable connector plug 49, of flexible,insulating, physiologically inert material, such as silicone rubber orthe like,is provided. The plug 49 serves to establish a physical andinsulated electrical connection between the housing 19, its electricalcontents, and a flexible elongated probe 51.

The probe 51 essentially comprises a long, flexible electrical conductor53, of stainless steel or the like. The conductor 53 is preferably woundin the form of a helix, as shown in FIG. 8. While the details of theprobe form no part of my invention, in practice it is preferred that thehelix 53 be formed of at least two parallel congruent concentriccontiguous helices made from two parallel wires, in the manner shown anddescribed in detail in copending U. S. Pat. application Ser. No. 41,980,filed on June 6, 1970 by Jean Bellerose for Flexible Probe Constructionand assigned to the assignee of this application.

The probe 51 further comprises an outer insulating coating 55, ofsilicone rubber or the like, which may be formed integral with the plug49. At or near the end of the probe 51 remote from the plug 49, there isformed an exposed electrode 59 of stainless steel, platinum or the like.The electrode 59 is bonded to the silicone rubber coating 55 andelectrically connected, as by soldering or brazing or the like, to thelead 53.

The flexible lead 53 is soldered or otherwise secured at its other endto a metal contact element 61 located in a suitable recess in the plug49. For example, the element 61 may be molded into the plug during themanufacture of the latter. As shown, a bore 63 in the element 61 mateswith corresponding bores 65 and 67 formed in the plug 49 to form apassage admitting a stiffener 69, such as a stainless steel wire or thelike.

As indicated in FIGS. 8 and 19, the stiffener 69 extends through thepassage just described and thence through the inside of the helicalconductor 53 up into engagement with the electrode 59. A suitable knob71, FIGS. 10 and 11, is secured to the stiffener 69 to facilitatemanipulation of the latter by an operator. In practice, the stiffener isinserted into the plug and up through the flexible probe 51 to stiffenthe latter sufficiently to permit it to be inserted into an artery orother body sinus to carry the electrode 59 to the desired operatingsite. The stiffener is then withdrawn to allow the probe to conformfreely to the convolutions of the sinus. Alternatively, it may bedesired to omit the stiffener and its function, and to draw the probeassembly into position by means of a forceps.

As best shown in FIGS. 10, the posts 39 and 41 are preferably formedwith flanges such as 75, between which sealing washers 77 of flexibleinsulating material are inserted. These washers 77 serve to cooperatewith bores 79 and 81 formed in the plug 49 to seal the posts 39 and 41and form a firm mechanical connection therewith.

A central passage 89 is formed in the post 41. Supported within thepassage 89 by means such as an intermediate insulating glass seal 91 isa contact assembly generally designated 93 and comprising a metal ball95 within a cage 97 and urged by a spring 99 into engagement with thecontact element 61. The conductor from which the cage 97 is formedextends down through the glass seal 91 and is soldered or otherwisesecured to the output lead 13 of the pulse transformer 7.

In practice, the plug 49, probe 51 and electrode 59 are installed in thebody, and the case 19 and its contents are separately installed. Theplug 49 is then engaged with the posts' 39 and 41. The plug is thensecured to the metal housing by means of the screw 47. Preferably, thescrew 47 is made of stainless steel covered with polytetrafluorethyleneor the like. The relatively large surface of the housing 19 makes amassive return electrode, so that the principal resistance offered bythe body to pulses produced by the pacer circuit occurs at the interfacebetween the electrode 59 and the adjacent tissue.

The apparatus of my invention is suitable for use in any applicationrequiring an implantable tissue stimulator. For example, in addition toits use as a cardiac pacer, it is also useful for stimulating othertissue, such as the carotid sinus nerve.

While I have described my invention with respect to the details of apreferred embodiment thereof, many changes and variations will occur tothose skilled in the art upon reading my description. Such changes andvariations can obviously be made without departing from the scope of myinvention.

Having thus described my invention, what I claim is:

1. In a cardiac pacer, the combination of:

a body stimulating electrode;

an electrical contact element;

an elongated flexible insulated conductor having one end connected tosaid electrode and'a second end connected to said contact element, saidcontact element being mounted in a surrounding plug member of flexibleinsulating material;

a pair of spaced parallel cylindrical apertures formed in said plugmember, one of said apertures communicating with said contact element;

a metal housing having a first terminal inside said housing and a secondterminal outside said housa pair of metal posts mounted on andprotruding from said housing, said posts extending into and closing saidapertures;

an insulated lead through one of said posts from said first terminal tosaid second terminal, said second terminal engaging said contactelement; and

a pulse generating circuit located in said housing and having an outputcircuit connected between said housing and said first terminal.

2. The apparatus of claim 1 further comprising means forming a threadedrecess in said housing; and

screw means cooperating with said recess and securing said plug memberto said housing.

3. A cardiac pacer, comprising:

a connector plug comprising a body member of flexible insulatingmaterial; a pair of spaced apertures formed in said body and extendingfrom one side thereof alo n parallel axes from sai side to terminationswt in said body member;

an electrical contact element mounted in said body and communicatingwith one of said apertures;

an electrode;

an elongated flexible conductor having one end electrically connected tosaid contact element and a second end connected to said electrode;

insulating means mounted on said flexible conductor;

a metal housing having a first terminal inside said housing and a secondterminal outside said housing;

a pair of metal posts mounted on and protruding from said housingextending into and closing said apertures;

an insulated lead extending through one of said posts from said firstterminal to said second terminal, said second terminal engaging saidcontact element; and

a pulse generating circuit located in said housing and having an outputcircuit connected between said housing and said first terminal.

4. The apparatus of claim 3, in which said flexible conductor comprisesa tubiform metal helix forming a flexible passageway closed at theelectrode end by said electrode, and further comprising means forming amating passageway through said body member, whereby a stiffener can bepassed into said flexible conductor to facilitate insertion of theelectrode in a body sinus.

5. A cardiac pacer, comprising:

a conductive metal housing having a generally plane side;

a pulse generating circuit mounted in said housing and having a firstoutput terminal connected to said housing and a second output terminalextending through and insulated from said housing;

apair of spaced mounting posts formed on said side and projecting fromsaid housing, said second output terminal extending through one of saidposts;

a flexible probe assembly comprising an exposed electrode adapted to beplaced in proximity to and in electrical contact with cardiac tissue tobe stimulated;

a connector plug comprising a body member of flexible insulatingmaterial having at least one generally plane side;

a pair of spaced, cylindrical apertures formed in said body forreceiving said posts and extending along parallel axes from said planeside to terminations within said body member;

an electrical contact element mounted in said body, communicating withone of said apertures, and connected to said second output terminal; and

an elongated flexible insulated cable connecting said electrode to saidelectrical contact element.

1. In a cardiac pacer, the combination of: a body stimulating electrode;an electrical contact element; an elongated flexible insulated conductorhaving one end connected to said electrode and a second end connected tosaid contact element, said contact element being mounted in asurrounding plug member of flexible insulating material; a pair ofspaced parallel cylindrical apertures formed in said plug member, one ofsaid apertures communicating with said contact element; a metal housinghaving a first terminal inside said housing and a second terminaloutside said housing; a pair of metal posts mounted on and protrudingfrom said housing, said posts extending into and closing said apertures;an insulated lead through one of said posts from said first terminal tosaid second terminal, said second terminal engaging said contactelement; and a pulse generating circuit located in said housing andhaving an output circuit connected between said housing and said firstterminal.
 2. The apparatus of claim 1, further comprising means forminga threaded recess in said housing; and screw means cooperating with saidrecess and securing said plug member to said housing.
 3. A cardiacpacer, comprising: a connector plug comprising a body member of flexibleinsulating material; a pair of spaced apertures formed in said body andextending from one side thereof along parallel axes from said side toterminations within said body member; an electrical contact elementmounted in said body and communicating with one of said apertures; anelectrode; an elongated flexible conductor having one end electricallyconnected to said contact element and a second end connected to saidelectrode; insulating means mounted on said flexible conductor; a metalhousing having a first terminal inside said housing and a secondterminal outside said housing; a pair of metal posts mounted on andprotruding from said housing extending into and closing said apertures;an insulated lead extending through one of said posts from said firstterminal to said second terminal, said second terminal engaging saidcontact element; and a pulse generating circuit located in said housingand having an output circuit connected between said housing and saidfirst terminal.
 4. The apparatus of claim 3, in which said flexibleconductor comprises a tubiform metal helix forming a flexible passagewayclosed at the electrode end by said electrode, and further comprisingmeans forming a mating passageway through said body member, whereby astiffener can be passed into said flexible conductor to facilitateinsertion of the electrode in a body sinus.
 5. A cardiac pacer,comprising: a conductive metal housing having a generally plane side; apulse generating circuit mounted in said housing and having a firstoutput terminal connected to said housing and a second output terminalextending through and insulated from said housing; a pair of spacedmounting posts formed on said side and projecting from said housing,said second output terminal extending through one of said posts; aflexible probe assembly comprising an exposed electrode adapted to beplaced in proximity to and in electrical contact with cardiac tissue tobe stimulated; a connector plug comprising a body member of flexibleinsulating material having at least one generally plane side; a pair ofspaced, cylindrical apertures formed in said body for receiving saidposts and extending along parallel axes from said plane side toterminations within said body member; an eLectrical contact elementmounted in said body, communicating with one of said apertures, andconnected to said second output terminal; and an elongated flexibleinsulated cable connecting said electrode to said electrical contactelement.